Investments of Operating Entities and Consolidated Funds - Equity Method Investments - (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Other investments	$ 141,180		$ 141,180		$ 157,279
Expense, equity method investments	900	$ 1,700	3,500	$ 6,800
Net Gains (Losses) on Securities, Derivatives and Other Investments
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments	4,100	(100)	$ 12,100	16,000
Equity Method Investments
Schedule of Equity Method Investments [Line Items]
number of investments			1
Other investments	42,370		$ 42,370		36,991
Starboard Value LP | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	15,939		15,939		12,501
Surf House Ocean Views Holdings, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	14,179		14,179		13,522
RCG Longview Debt Fund V Partners, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	8,487		8,487		7,256
Healthcare Royalty GP II, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	190		190		354
Healthcare Royalty GP, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	340		340		583
RCG Longview Management, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	961		961		656
RCG Longview Debt Fund IV Management, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	331		331		331
RCG Kennedy House, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	136		136		183
Healthcare Royalty GP III, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	626		626		208
RCG Longview Equity Management, LLC | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	114		114		114
Healthcare Overflow Fund GP, LLC [Member] | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	76		76		68
Equity Method Investee, Other | Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Other investments	$ 991		$ 991		1,215
Minimum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	57.00%		57.00%
Clawback Obligation [Member]
Schedule of Equity Method Investments [Line Items]
Other Commitment					6,200
Clawback Obligation [Member] | RCG Longview Partners II, LLC
Schedule of Equity Method Investments [Line Items]
Other Commitment	$ 6,200		$ 6,200		$ 6,200
Operating Companies [Member] | Equity Method Investee, Exceeded Threshold for Income Test [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Revenue	9,734	24,865	27,646	27,592
Equity Method Investment, Summarized Financial Information, Expenses	0	0	0	0
Equity Method Investment, Summarized Financial Information, Gain (Loss) on Investments	88	116	163	290
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 9,822	$ 24,981	$ 27,809	$ 27,882